Measuring Forster resonance energy transfer between fluorescent nanodiamonds and near-infrared dyes by acceptor photobleaching

Fluorescent nanodiamonds (FNDs) containing negatively charged nitrogen-vacancy centers as fluorophores are promising far-red biolables. The fluorophores are perfectly photostable, showing neither photobleaching nor photoblinking, and are useful as Forster resonance energy transfer (FRET) donors. This work demonstrates that it is possible to achieve an average FRET efficiency of up to 30% between a single 23-nm-sized FND (emission maximum similar to 685 nm) and multiple near-infrared dye molecules (absorption maximum similar to 774 nm) co-embedded in a poly-L-lysine matrix. The efficiency was determined by measuring the increases in both fluorescence intensity and lifetime of the FRET donor (i.e. FND) after photobleaching of the FRET acceptor (i.e. IRdye-800CW). Monte Carlo simulations indicate that on average, there are similar to 9IRDye molecules located in close proximity to each FND particle. (C) 2011 Elsevier B.V. All rights reserved.